High side pressures are very important. There are commonly available adapters that will work with the smaller Ford R12 fitting and convert it to an R-134 fitting.
R134 high side pressures are much higher than for R12. As a general rule, you want to see no more than 3x ambient temp for high side pressures at 1500 RPM with the blower on high and outside air selected. For example, if it is 90 degrees out, you'd look for a max of 270 psi on the high side.
Also, R134 conversions usually take only about 80% of the charge listed for R12. Overcharging can and will cause high vent temps and blown blow off valves at the compressor.
If the fan clutch is weak, you won't be getting the airflow thru the condenser that is required....especialy with R134. Even at road speeds, the fan needs to be puling to get air thru the condenser.
Low side pressures should get down into the 20's for best cooling. The R134 a/c cycling switches are generally set to shut the compressor off at around 25 psi. If 44 psi is as low as your low side will go, you are either overcharged or the compressor is weak, or the fan isn't pulling air thru the condenser.
All this assumes at least one full hour of vacuum applied to the system and NO air contamination. This includes any air in the a/c gauge lines. They must be bled prior to connecting to the system, or a big gulp of air goes right in with the refrigerant.
Greg